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Family Man

oil blowing out breather tub 07 yz450f

9 posts in this topic

I recently rebuilt the top end of my 07 yz450f, 20hrs ago on the meter. The Cylinder had no cross hacthing left, so I bought a ball hone and and honed the cylinder, put in a new piston and rings and timing chain, and had the head redone. maybe the cylinder was to far gone? It has begun blowing out oil from the breather. Are there any other things that can cause oil to blow out the breather besides worn rings/cylinder, I dont think its overfilled put in 1000cc of oil. The bike has tons of hours on it. Thinking if it does need a cylinder I might do the crank too and maybee big bore and stroker it to 500cc. 

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if u didn't measure the bore I don't know why your did the rebuild ?  snap gauges are cheap at HF

  even when your dropped the ring in and measured the end gap should have given you an idea if it was to worn for a hone

but it sure sounds like blow by from the rings

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It ran  good for 18 hours after the rebuild. Then I started noticing it was spraying oil out the breather tube. It doesn't smoke but I'm loosing oil. Figure teardown as most threads on this board point to blowby.

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One of the hazards of running the cylinder too long is that the Nikasil can wear all the way through, and the rings start running on aluminum.  Not a good thing.

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Ordered a a new cylinder works cylinder and piston kit, standard bore and compression, should be good to go after that.  I think the old cylinder was just plain wore out. 

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Ordered a a new cylinder works cylinder and piston kit, standard bore and compression, should be good to go after that.  I think the old cylinder was just plain wore out. 

keep us posted

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 Thinking if it does need a cylinder I might do the crank too and maybee big bore and stroker it to 500cc. 

any conclusion  on the crank ?

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crank is still with in limit side to side, and no up and down play. Hopefully it'll hold up.

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